1. Field of Invention
This invention concerns a load driving system which can be used in a camera to wind a film or to charge the camera shutter mechanism.
2. Description of Related Art
A conventional load driving system, as described in published Japanese patent application 60-194433, provides two gear trains with different reduction ratios between a motor output shaft and a load. The motor is capable of rotating in a forward direction and a reverse direction. Either a first gear train or a second gear train is selected, based on the rotational direction of the motor. The first and second gear trains provide two sets of features best suited for two different situations. For example, the first gear train's reduction ratio is set to obtain a maximum output while the second gear train's reduction ratio is set to obtain a maximum efficiency. When a battery discharge level is low, the first gear train is selected by rotating the motor in the first direction to obtain the maximum output and to increase the driving speed of the load. When the battery discharge level is high, the second gear train is selected by rotating the motor in the reverse direction to obtain maximum efficiency.
A pinion gear is installed on the motor output shaft. This pinion gear is shared by the first and second gear trains. The rotation from the pinion gear is transmitted from the pinion gear to one of the first and second gear trains through a clutch. However, the clutch is powered by the motor through a third gear. This third gear is common to both the first and second gear trains. Since the third gear can have the features of only one of the sets of features of the first and second gear trains, the full benefit of having two gear trains is not achieved. Furthermore, in conventional load driving systems, the problem of gear motion noise is completely ignored.